Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $82.74   13.438%   $93.8586   $93.86   $93.85   $93.90  
  Purchase #2 $120.41   9.321%   $131.6334   $131.63   $131.65   $131.60  
  Purchase #3 $115.62   3.536%   $119.7083   $119.71   $119.70   $119.70  
  Purchase #4 $37.56   9.720%   $41.2108   $41.21   $41.20   $41.20  
  Purchase #5 $218.51   5.609%   $230.7662   $230.77   $230.75   $230.80  
  Purchase #6 $100.63   6.637%   $107.3088   $107.31   $107.30   $107.30  
  Purchase #7 $33.80   6.354%   $35.9477   $35.95   $35.95   $35.90  
  7 purchase totals = $709.27       $760.4338   $760.44   $760.40   $760.40